Spring devices for vehicle seats are known in particular for attenuating a height excursion of the vehicle seat when travelling over uneven road surfaces, such as potholes. EP 1 188 608 A1 discloses an active suspension system for sprung vehicle seats, in which a pneumatic offload device and a hydraulic actuating member are arranged between a seat part and a lower part that is connected to the vehicle, along with a mechanical flexible connection device. Both the pneumatic offload device and the hydraulic actuating member are controlled by a control device as a function of a seat error signal, which is generated for example by a jerky height adjustment of the seat part.
Such hydraulic actuating members require a connection to the on-board power supply of the vehicle, in particular of a utility vehicle. Such a connection results in the function of the active suspension of the vehicle seat being dependent on the function of the on-board power supply and in particular the parameters thereof, so that it is necessary to match the parameters of the suspension system to the parameters of the on-board power supply and thus to adapt the system to the respective utility vehicle.
Moreover, air springs are known which have a force-path air spring characteristic that runs linearly, the incline of which can be changed as a function of the design of the air spring and of an applied additional air volume, but which have the same incline over the entire force path air spring characteristic. In such air springs, use is generally made of additional air volumes that are kept constant, which as actual air volume of the air spring are associated with the air spring moving in and out.
Such additional air volumes which are kept constant result in a swinging back of the seat part into a central position of the force-path air spring characteristic not being possible when the air spring is set with a force-path air spring characteristic having a small incline, since friction forces within the spring device as a whole are greater than a return force within the force-path air spring characteristic.
On the other hand, when the spring device is designed such that the return force is greater—that is to say a greater incline in the air spring characteristic is set—a comparatively hard damping is achieved both in the middle travel region and in the end of travel regions of the air spring.
Moreover, when using an air spring in an air spring characteristic range with a small incline—the so-called comfort range—which requires that a large additional volume be switched on, reaching of the end stops in the end of travel regions of the air spring in the event of large in and out movements becomes probable on account of a high degree of unevenness, as a result of which there is a reduced seating comfort for the user of the vehicle seat. The setting of a comfort range is generally desired in the case of air springs for vehicle seats on account of better transmission values and the higher degree of comfort resulting therefrom.